NewDBKeeper creates and returns a new DBKeeper instance with the provided database, logger, and retrier.

NewFileKeeper creates and returns a new FileKeeper instance with the provided configuration, logger, and retrier.

NewMemStorage creates and returns a new MemStorage instance.

OpenDB opens a database connection.

DBKeeper is a struct that manages database operations and holds a SQL database connection, a logger for logging operations, a retrier for handling retry logic, and a mutex for synchronizing operations.

FileKeeper is a struct that manages file operations and holds a logger, the path to the file storage, a retrier for handling retry logic, and a mutex for synchronizing operations.

MemStorage is a struct that manages in-memory storage operations, periodic flushing to external storage, and logging.

State represents the in-memory storage state containing metrics and a mutex for synchronization.